Which hormone is primarily involved in regulating thirst and water retention?

The hormone primarily involved in regulating thirst and water retention is antidiuretic hormone (ADH), also known as vasopressin. ADH is produced in the hypothalamus and stored in the posterior pituitary gland. Its primary function is to promote the reabsorption of water in the kidneys, which helps concentrate urine and reduce water loss from the body.

When the body is dehydrated or when blood osmolarity rises (indicating a higher concentration of solutes in the blood), ADH is released into the bloodstream. It acts on the renal tubules in the kidneys, increasing their permeability to water and encouraging water reabsorption back into the bloodstream. This process reduces urine volume and helps maintain proper hydration levels, thereby regulating thirst effectively.

In contrast, the other hormones listed play different roles in the body. Insulin primarily regulates glucose levels and does not have a direct role in water regulation. Cortisol, a steroid hormone, influences metabolism and immune response but is not directly involved in managing thirst or water retention. Thyroxine, produced by the thyroid gland, is mainly responsible for regulating metabolism and energy balance, rather than fluid balance. Therefore, ADH is the key hormone for managing thirst and water retention in the body.